Parents are not meant to bury their children. So we know every mom and dad shares the heartbreak of the parents of Amar Diarrassouba — the 6-year-old Harlem boy crushed by a truck’s back wheel while walking to school with his brother.

In the hours since, this case has moved from the tragic to the criminal. Police Commissioner Ray Kelly says that 25 minutes before the truck hit, crossing guard Flavia Roman falsely called in to police to say she was on duty. That would mean Roman was also lying after the accident when she claimed she had been on a short bathroom break when the boy was killed.

No system is perfect. Even with a guard on duty, there can still be accidents. And police certainly need to investigate whether the driver of the truck was in any way at fault.

But Roman has put herself in a wholly different category. Not only did she abandon the schoolchildren she was supposed to protect, police say she lied about it. Some parents say they have seen no guard at her intersection before. Others say they have watched Roman gabbing when she should have been doing her job.

Now it’s up to the city. New York’s criminal-justice system has a duty to hold this guard liable for her words and her actions. The authorities need to probe this case thoroughly — and pursue the full measure of punishment allowed by the law.

New York City employs more than 2,000 crossing guards to keep its schoolchildren safe as they navigate Gotham’s busy streets and cross dangerous intersections. Those who take these jobs take on an important public trust. Amar Diarrassouba’s death is a reminder of the terrible price that the innocent pay when someone in a position of public trust blows off that responsibility.